Electrodynamic particle separator

ABSTRACT

Charged particles such as ions in solution or suspended solids having a natural or induced electric charge are separated from or concentrated in the fluid medium in which they are contained. The fluid medium is conducted through a non-magnetic duct through which an intense magnetic flux rotating at high velocity is directed. Particles having opposite polarity charges are deflected in opposite directions and concentrated under the influence of Lorentz forces which are defined as F q V X B, where F is the deflecting force vector, q is the magnitude of the charge on a particle, V is the velocity vector of the particle and B is the magnetic flux vector. A multiported analyzer near the duct exit divides the streams which contain the concentrates from the dilute stream. Means are provided for regulating the flow volume through the ports.

United, States Patent Lang ELECTRODYNAMIC PARTICLE SEPARATOR Inventor:James I. Lang, Oneida, Wis.

Assignee: John F. Sylvester, Green Bay, Wis. Filed; May 5, 1971 Appl.No.: 140,443

US. Cl. ..209/212, 209/219, 209/232, 210/222, 55/100 Int. Cl. ..B03cl/l2, B01d 35/06 Field of Search ..209/219, 232, 220, 222, 214, 209/215,39 YO, 223, 227; 210/222, 223;

References Cited UNITED STATES PATENTS lO/l966 Begor ..209/222 Orbeliani..209/223 Sunnen ..55/100 X Gaeta ..73/54 Auampato ..210/222 X Roberts..210/223 X Weston ..209/214 Moragne ..209/232X [4 1 Sept. 26, 1972s/1922 McCarthy ..209/212 l/l966 Moldy ..2o9/212x Primary Examiner-FrankW. Lutter- Assistant Examiner-Robert Halper At t0rneyWiviott &Hohenfeldt [57] ABSTRACT Charged particles such as ions in solution orsuspended solids having a natural or induced electric charge areseparated from or concentrated in the fluid medium in which they arecontained. The fluid medium is conducted through a non-magnetic ductthrough which an intense magnetic flux rotating at high velocity isdirected. Particles having opposite polarity charges are deflected inopposite directions and concentrated underlhe intlgence of Lorentzforces which are defined as F'= q V F, where F is the deflecting forcevegpr, q is the magnitude of the charge on 3 particle, V is the velocityvector of the particle and B is the magnetic flux vector. A multiportedanalyzer near the duct exit divides the streams which contain theconcentrates from the dilute stream. Means are provided for regulatingthe flow volume'through the ports.

20 Claims, 7 Drawing Figures PATENTEDssrzs m2 sum 1 or z JNVENTOJAMES 1. BY/WM aw ATTORNEY PATENTEDSEPZB 1912 SHEU 2 [IF 2 'INVEINTORJAM ES 1. LANG B 70mm my" ATTORNEY ELECTRODYNAMIC PARTICLE SEPARATORBACKGROUND OF THE INVENTION Many industries today are faced with theproblem of separating fine suspended solids and dissolved ions fromfluids. Sometimes it is desired to concentrate or separate fineparticles because they or the fluid in which they are suspended haveintrinsic economic value. In other cases separation is desired because afraction of the fluid is intended for disposition as a waste which wouldbe considered a pollutant if discharged into a stream, a lake or theatmosphere. There have been several prior methods of separating fineparticles from fluids but none is universally applicable. For instance,electrostatic precipitators remove solid particles having a certain sizerange from a gaseous suspension but they are not effective for removingparticles from a liquid. Various kinds of mechanical filters have alsobeen devised but these usually have limited capacity and requirefrequent cleaning or replacement of the filter elements. They alsoimpose a severe restriction on the flow rate of the fluid medium passingthrough them in which case their use may adversely affect the industrialprocess to which they pertain. Various types of magnetic separators havealso been devised, but their use is limited to particles which aremagnetically susceptible.

Another process that is used for separating particles is electrophoresiswhich involves immersing a pair of oppositely polarized electrodes in afluid which entrains particles whose separation is desired. Negativelycharged particles are thus attracted to the anode and positively chargedparticles to the cathode so that separation or, at least, concentrationof the suspended material occurs near the electrodes. Electrophoresisapparatus, however, is subject to electrochemical effects such as theproduction of gases around one or both of the electrodes, thus changingthe potential gradient and the effectiveness of the apparatus.

It should be apparent upon consideration of the aforementionedcommercially available devices that there is a critical need for-amethod and device that will separate or concentrate ions, complexes,organic particles such as proteins, inorganic particles and colloidalsubstances from afluid suspension. A typical and heretofore unfulfilledapplication of such a device is to separate whey and other undissolvedorganic particles from the fluid wastes which are incidental to theproduction of cheese. Whey has commercial value but it is oftendischarged as waste and constitutes a principal source of pollutionbecause its separation has been difficult. Whey is a proteinoussubstance which has an intrinsic electric charge so that it can beeffectively removed, like many other substances, from a liquidsuspension bythe new electrodynamic particle separator which will bedescribed below.

SUMMARY OF THE INVENTION According to the present invention, a fluidmedium containing ions. and suspended solids, hereinafter called chargedparticles for brevity, is conducted through a curved non-magnetic duct.Adjacent opposed sides of the curved duct are rotating magnets whichcreate magnetic flux lines that are transverse to the flow path of thefluid in the duct. Relative motion is obtained between the chargedparticles in the suspension and the magnetic field by rotating themagnets at high velocity. The electrostatic charge on the particlesreacts with the magnetic field in such manner that particles which arecharged with one polarity are deflected radially inwardly and particleswhich are charged oppositely are deflected radially outwardly so as tocreate a concentration of these charged particles on the inner and outerinterior peripheries of the duct. If all particles have the same chargethey will, of course, deflect or migrate in one direction only. Thephysical laws relied upon to effect particle separation are expressed bythe Lorentz equation F qE qVXfi as will be discussed more fullyhereinafter. Fluid flow through the duct is preferably laminar sinceturbulent flow produces undesirable mixing. The particles are constantlyurged in one direction or another in which case they migrate towardopposite walls where they become concentrated in separate streams by thetime they are near the exit. The exit end of the duct is provided with atransverse multiple port means to separate the concentrate streams whichfollow the interior and exterior peripheries of the duct from the moredilute central stream. The duct may be subdivided into several mainstreams which each have their own means and which are independent ofeach other. The dilute central stream usually flows from a central portof the port meansl The device is adapted to conduct the concentrate andthe dilute portions of the fluid along separate paths. i

' Charged particles having sizes on the order of .01 to microns may beseparated or concentrated with the new device. Even magneticallysusceptible particles can be separated by the new electrodynamictechnique provided the particles are large enough, such as about 10microns, to accept sufficient charge. In such case, the electrodynamicreaction with the rotating magnetic flux will overwhelm the forces ofsimple magnetic attraction which predominates in prior art magneticparticle separators. Moreover, the relative velocity between theparticle suspension and the rotating magnetic field in prior magneticseparators is, perhaps, up to about 10 feet per second, whereasin thenew electrodynamic separator relative linear velocity between theflowing charged particles and the magnetic field is in the realm of 100to 1000 feet per second or even greater. Thus, field rotation ratesranging from about 1000 to 100,000 revolutions per minute arecontemplated in conjunction with fluid suspensions that flow in the samedirection or counter to the magnetic field rotational direction.Magnetic flux densities are on the order of 1000 to 25,000 gausses.

A general object of this invention is to provide a new velocity betweena magnetic field and the particles not by accelerating the particles tohigh speed but by revolving magnetic flux at high speed.

More specific objects are to relate magnetic rotation,

fluid flow rate, and outlet analyzer geometry in an elec- How theforegoing and other more specific objects are achieved will appear fromtime to time throughout the course of the ensuing description of apreferred embodiment of the invention taken in conjunction with thedrawings. i

DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation view, partly invertical section, of an embodiment of the new particle separator;

FIG. 2 is a transverse cross section, with parts omitted, taken along'aplane corresponding with 2-2 in FIG. I;

FIG. 3 is a particle stream exit port means shown in a cross sectiontaken on a line corresponding with 3-3 in FIG. 2;

FIGS. 4 and 5 are alternative forms of particle stream exit analyzers;

- FIG. 6 is a side view of a fragment of a modified duct for use in aparticle separator; and,

FIG. 7 is a cross section taken on a plane corresponding with 7-7 inFIG. 6.

DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT Refer to FIG. 1. The newparticle separator cornprises a'shaft 10 which is supported inspaced-apart journals 11 and 12 which are each on suitable mounts l3 and14. Shaft l0-may be caused to rotate at high speed by any suitable primemover. Shaft rotational speeds up to 100,000 rpm may be used in somecases with speeds of 20,000 to 30,000 rpm being most usual. This may beaccomplished by conventional means such as a steam or air turbine or arelatively low speed electric motor and a step-up gear train, not shown.Another method-of obtaining high shaftrotational speeds is to drive theshaft with a directly coupled two-pole induction motor which isenergized from a voltage source at a frequency which is some multiple ofthe normal60 Hz shaped pole pieces 17 and 18. These pole pieces may bemade of soft iron or other ferromagnetic material which has high"magnetic permeability. They may also be strong permanent magnets. Therespective pole pieces terminate in flat annular pole faces 19 and 20which define an air gap 21 between them.

Fixed to shaft 10 in the space created between hubs 22 and 23 of thepole pieces is a cylindrical core 24 which also preferably has highmagnetic permeability. The annular space surrounding core 24 is occupiedby many turns of insulated wire constituting an electromagnet coil 25.Coil 25 is suitably insulated from core 24 and restrained by suitablebanding, not shown, to prevent centrifugal destruction of the coil whenit is rotated at high speed. Fastened to the axial ends of the magnethubs 22.and 23 are two similar slip ring-assemblies 28 and 29. Theseslip rings are conventional in that they comprise an insulatingcylindrical disk 30 which is centrally bored to fit over shaft 10 asexemplified by assembly 28. The insulating disk is fastened to the axialend of magnet hub 22 by means of circumferentially spaced apart screws31. Pressed or molded on the outer periphery of insulating disk 30 is ametal slip ring 32. Slip ring 32 rotates and makes sliding contactagainst a graphite brush 33 which is supported in an insulating brushholder 34. The brush holder has the usual internal springs, not shown,for urging the brush against slip ring 32. The bores of the hubs 22 and23 may be slotted axially as at35 and 36 respectively, toprovidepassages for lead wires that. connect the opposite ends of coil25 to the slip rings. A conductor, not shown, runs through the interiorof each brush holder 34, 34' and connects with a source of d-c power,not shown. Generally, magnetic flux density will be on the, order of1000 to 25,000'gausses whether the flux is produced with permanentmagnets or electromagnets.

Interposed between pole faces 19 and 20 in air gap 21 is a curved duct40 of non-conducting and non-magnetic material such as plastic. The ducthas a rectangular cross section with rounded corners as shown in FIG. 1but it may be round or otherwiseshaped cross sectionally provided themagnetic pole pieces are suitably shaped. The center channel 46 of thecurved duct 40 is substantially coincident with the axis of shaft 10 andsurrounds it. The duct is supported on a pedestal 41 which is merely.symbolized and may take many forms. From the description thus far, itshould be evident that when coil 25 is energized from a d-c source,cupshaped pole pieces 17 and 18 will be magnetized and will'serve aspart of a magnetic circuit which is interrupted annularly by air gap 21.In other words, the magnetic lines of force will extend across gap 21between pole faces 19 and 20 and in so doing will traverse duct 40axially to produce a substantially uniform distribution of magnetic fluxthrough the duct. Accordingly, when shaft 10 and pole pieces 17 and 18are rotated at high speed, the flux lines bridging gap 21 and the ductwill be cut by any charged particles that are standing or are in motionwithin duct 40. The rate at which the flux lines are cut by any selectedparticle depends on the rotational velocity of the pole pieces andtheflow direction and velocity of the fluid within the duct. As ageneral rule, high relative velocity between the magnetic field andparticles will produce a greater electrodynamic interaction between theflux and the particles but as will appear later, optimum particleseparation efficiency may occur within a comparatively narrow relativefluid velocity range.

Generally, magnetic fluxmoving at a linear velocity in the range of to1000 feet per second is contemplated. The most likely maximum linearvelocity limit would be the speed of sound in air. Exceeding the speedof sound would require extremely high magnet rotational speeds and wouldgive rise to difficult engineering and design problems as is well known.

A vertical section taken through duct 40 in a plane which is normal tothe shaft axis is shown in FIG. 2. The axis of shaft 10 coincides withthe center of the full circle 42 .which defines the radially interiorwall of the duct. The axial or sidewalls of the duct are marked 43 and44, the latter appearing only in FIG. 1. The radially displaced outerwall of the duct is marked 45 and the annular duct channel is marked 46.It should be observed that channel 46 is substantially a complete circleor nearly 360 in angular measurement about the axis of shaft 10, so themagnetic flux acts on the fluid suspended particles for the maximumamount of distance and time.

FIG. 2 shows that the duct has a radial extension 47 whose width issubstantially the same as that of the duct in this example. Extension 47has a lengthwise partition wall 48 which divides the extension into afluid inlet channel 49 and multiple fluid outlet channels comprising aninside annular channel 50, a central channel 51 and an outside channel52. Fluid may exit from the duct and the last named three channelsthrough holes 53, 54, and 55. Fluid enters the duct through an inlet 56and follows a path through inlet channel 49 whereupon it may enter andcirculate around main duct channel 46. There is preferably a diverter 57located in duct channel 46 to minimize stagnation but not to causeturbulence since it is desirable that the fluid suspension flowingthrough duct channel 46 be laminar rather than turbulent.

For reasons which will be explained later, it is desirable to regulatethe quantities flowing in the outer annular concentrate stream 52 andthe inner annular concentrate stream 50 as compared with the quantityflowing in the more dilute central stream 51 and to coordinate thesequantities with fluid velocity and the area of the exit ports. Toprovide this function, a throttle valve 58 is used to control jointlythe effluent from channel 50 and its outlet 53 and channel 52 and itsoutlet 55. Thus, valve 58 has its input side connected with outlets 53and 55 by means of pipes 59 and 60 which are merely symbolized asstraight lines. There is also a valve 61 which is connected with centralstream outlet 54 by means of a pipe 62 which is symbolized by a straightline.

In accordance with known physical laws, when a fluid suspension ofcharged particles is conducted through duct 46 as, for example, in thedirection of the arrow 63 while magnets 17 and 18 are rotating withshaft 10, the charged particles will cut the flux lines relativelybetween pole faces 19 and 20 and therewill be an electrodynamicinteraction between the magnetic flux and the particles. The particlesmay be treated as having a velocityvector and the flux lines may betreated as a vector quantity. The force produced on the particles willthus be a vector quantity whose direction will be perpendicular to theplane defined by the velocity and flux vectors. The magnitude of theforce is proportional to the sine of the angle between the velocityvector and the flux. Suspended particles which are charged with onepolarity will, therefore, be deflected toward inner wall 42 of the duct,and particles having the opposite polarity charge will be deflectedtoward the outer wall 45 in this embodiment. These particles are actedupon by the magnetic field substantially during the particles entiretransit time in duct channel 46 in which case the oppositely chargedparticles will migrate or be deflected toward the opposite walls of theduct and by the time the particles arrive in the exit region 64 of theduct they will be highly concentrated along the radially separatedinsides of the duct walls. 0n the other hand, the central stream of thesuspension will have had charged particles removed and will be moredilute than when the fluid suspension was admitted to the interior ofduct 46. The two concentrate streams may be discharged separately orjointly as through valve 58 and its associated piping as explainedearlier. The central diluted stream may be discharged through valve 61as previously explained.

The physical law governing particle separation in accordance with theinvention and as outlined in the preceding paragraph is expressed by theLorentz equation:

where F is the force on the charged particles, the force being a vectorquantity, q is the electric charge on a particle, V is a vector quantityrepresenting the relative velocity of the particle with respect to themagnetic flux is the magnetic flux vector. The magnitude of the VXBvector is 'ven b y VBSinO, where 0 is the angle between vectors and B.Any consistent set of units may be used in connection with the abovegeneral form of the Lorentz equation but the MKS system of units isusually implied as is the case herein. In the absence of an electricfield, as in the preferred embodiment of the present invention, the qEterm may be disregarded.

In accordance with the Lorentz equation, a charged particle which is ina relatively moving magnetic field will be deflected at a right angle toboth the velocity vector V and the field vector l3. As 0, the anglebetween the velocity vector and the flux vector, approaches zero, thesine of 0 approaches zero and the component of the velocity which isnormal to the flux lines approaches zero. Hence, the deflecting forceapproaches zero. When 0 approaches the sine of 0 approaches one and thecomponent of velocity which is normal to the flux lines is maximum inwhich case the deflecting force is maximum.

The trajectory of the individual charged particles in the fluid is morecomplex than would be the case if the magnetic field and chargedparticles were interacting in a vacuum. The trajectory of a particlefrom any given position in stream toward a duct wall is affected byintermolecular forces of an electric nature which originate from thefluid medium. In addition, the relative velocity vector of a particlewith respect to the magnetic flux lines may be afiected by a velocityvector which is additive or subtractive depending on whether the fluidis flowing in the direction of rotation of the magnetic field or counterto it. The dynamics of viscous flow dictate that fluid velocity will bemaximum at the center of the duct and reduced to substantially zero atthe walls of the duct in which case the fluid velocity component of thetrajectory will be affected cor respondingly. The result of thesevarious effects is for the particles to drift or migrate toward the ductwalls rather than to follow the trajectory that they would follow if theparticles were in free space and influenced solely by Lorentz forces. lnany case, however, where the circumferential length of the duct isadequate there will be a concentration of oppositely charged particlesat the respectively radially inward and radially outward walls of theduct and these particles will be swept along by the fluid flow towardthe exit region of the duct where they will be at maximum concentration.

There are some additional phenomena to which attention must be given.For instance, when particles with opposite charges begin to concentrateon the opposite walls of the duct, a more sparse population of chargedparticles exists in the central stream. The collective force of theconcentrated charges tends to repel particles withlike charges thatremain in the central stream. These forces must be subtracted from theforce which puts the particles in a trajectory that concentrates them.Fluid flow also has an effect on the direction and rate at which theparticles will drift or migrate to the duct walls. Fluid flow causes aradial pressure gradient which results in a secondary flow of chargedparticles. Secondary flow of particles is usually in two closed loopswhich have the same direction in the center of the duct as they flowtoward the'outer duct periphery and an opposite common directioncentration of charges in the central annular region as well as on thetwo peripheral annular regionsaMore information on the nature ofsecondary flow resulting from afluid flowing around a curve isobtainable in the book Rouse, I-I. & Howe, J. -W., Basic Mechanics ofFluids, John Wiley & Sons, Inc; 1953, p. 157, Library of CongressCatalog Card No. 53-6518.

Some charged. particles, particularly colloids, have exhibited apropensity to collect almost exclusively on the internal peripheralwalls and on the radially spaced sidewalls with a central diluted regionbeing framed or surrounded by a complete rectangle of concentrates.Tests made on dilute solutions or dispersions showed that the particleswere concentrated almost exclusively on the internal surfaces of theradially spaced duct walls.

The foregoing discussion provides a basis for going ahead with adescription of the multi-ported means which is interposed inside of theduct in the vicinity of exit region 64. The port means used in the FIG.1 and 2 embodiment comprises a large central opening 67 which isrectangular in'cross section as'can beseen in the cross sectional viewof FIG. 3. This rectangular port 67 is defined by spaced apart end walls68 and 69. The end walls also serve as one side of narrow concentrateports 70 and 71 through which the concentrates exit from duct 46. Thisis a configuration which has been successfully used in connection withseparating proteinous particles from a liquid suspension.

An alternative form. of exit port means which is useful forconcentrating certain types of particles is shown in FIG. 4 oriented asit would be if it wereviewed toward the line 3-3 in FIG. 2. In the FIG.4 embodiment, there is a rectangular central port 73 through which thesolution which has been deprived of most of its charged particles flows.This central port is bounded by a continuous rectangular wall 74 whichalso defines a rectangular annulus 75 through which the concentratedcharged particles exit. This exit port means configuration is one of theoptions a user may request for treating a particular suspension which ismost efficiently analyzed with this type. For instance, this type ofport means may be most effective for treating colloidal suspensions.

An alternative form of port means is depicted in cross section in FIG.5. This port means has two central ports 76 and 77 which are defined byrectangular tubular partitions 78 and 79. There are also several annularregions 80-84 through which the concentrates exit. Concentrations ofcharged particles accumulate in the annular regions 80-84. This designis particularly effective in removing the charged. particles'which tendto follow the central annulus 83 due to secondary flow which.resultsfrom polarization as discussed above. In reality, the presenceof the median annular duct 83 has the effect of reducing polarizationsince charged particles of one polarity will tend to flow in a singledirection along region 83. This charge and concentrate distributionpattern, of course, actually occurs along the main circular duct channel46 and the port means configuration is merely that which will mosteffectively discharge the concentratw without remixing them with themore dilute solution. The multi-ported means shown in FIG. 5 hasexhibited high efficiency in removal of whey from the liquid milkresidue which is a by-product of the cheesemaking process.

7 It should beunderstood that the duct need not be rectangular in crosssection. Particle separation can be obtained in ductsthat have acircular or an elliptical cross section and other configurations too. Arectangular cross section with slightly rounded corners appears to havevery good separating properties. Various cross sectional shapes can bemade having an area for the dilute part of the stream and isolatedannular areas for the concentrates.

The intemaldimensions of the main duct channel influence chargedparticle separation efficiency. The

greater the radial dimension or height I. of the duct in comparison withthe axial dimension or width W of the duct, the'larger will bethestorage area for charges swept to the sides of the duct by secondaryflow. If W is relatively small, the air gap between the magnetic polefaces may be small in which case the reluctance of the flux path isreduced and the flux B will be advantageously more intense. Findingsthus far indicate that if the ratio of L to W is very much greater than5:1 flow instability results and the separation process is defeated. Ifthe ratio of L to W is less than 1:1, the air gap is too large, fieldintensity across the duct suffers and the charge storage'area is toosmall for good separation. It has been determined, however, thatpolarization and secondary flow become unstable at large ratios, of L:Wsuch as 10:1. The preferred ratio range of L:W appears to be 1.5:1 to5:1 although it has not been con-, firmed that these are the absolutelimits for all fluids and all types of charged particles.

Anyone desiring to design a particle separator such as is describedabove might assume that at very low.

tion quickly occurs, stopping further separation. On the other hand, atexcessively high flow rates, the residence time of the charged particlesin the magnetic field is too short for good separation. It is not easyto specify an intermediate fluid flow rate which will optimize particleseparation because this will depend on a number of selectable designparameters such as the radius of curvature of the duct median line andthe cross sectional dimensions of the duct.

When fluid flows in a laminar condition within an enclosed duct, avelocity gradient across the flow path is typically parabolic whichmeans that the flow near a wall is slowed by friction between the walland the fluid. Superimposed on the velocity gradient in this device isthe secondary flow, which makes the velocity gradient steeper than thatexisting in straight channels. it is, of course, desirable that thelinear fluid velocities at both dilute solution exit ports such as 76and 77 in FIG. be equal to the velocity of the annular exit ports forthe concentrates such as ports 80-84 in this figure. To obtain thisequality, throttle valves 58 and 61 are provided. These valves can beadjusted to balance the flow asrequired. It has been found that optimumseparation occurs when the ratio of the area of the dilute exit port tothe area of the annular concentrate exit ports is in a range ofabout1.5:1 to 5:1.

- It should be apparent that flow of the fluid medium through the ductshould be laminar rather than turbulent if charged particle separationor concentration is to be successful. Those who are knowledgeable influid mechanics will appreciate that whether flow is laminar orturbulent depends on the Reynolds number R and the Dean number D of thesystem. Generally, if the Reynolds number is 2000 or less, flow will belaminar in straight flow but with radial geometry laminar flow may existat Reynolds numbers which are 3.5 or more times as high: As is known,when the Reynolds number, which is dimensionless, is determined for aparticular design it can be used as a criteria for maintaining laminarflow in designs that are scaled up or down as long as fluids of the sameviscosity are involved and the dimensions and flow rates areproportional.

The general expression for the Reynolds number is:

where V is the fluid characteristic velocity, R is the hydraulic radiusof the duct defined as its cross sectional area directed by the wettedperiphery, p(rho) the density of the fluid and (mu) the viscosity of thefluid. This is an expression of the ratio of inertial shear forces toviscous shear forces in a flow system and predicts that if the Reynoldsnumber is high, inertial forces will dominate, provided viscosity islow, and if low, viscosity will dominate. For pipe flow, 4R is equal tothe pipe diameter, but for a rectangular duct, as is the case here,

where L is duct length, and W is duct width.

The Dean number D is another similarity parameter that is useful forpredicting onset of turbulent flow when curvature of the flow path isimportant. The general expression is:

where R, is the Reynolds number, R is hydraulic radius of the duct and rthe radius of curvature of the duct center line. Thus, onset ofturbulent flow in a curved duct depends on the Reynolds number R, andthe ratio of ZR /r. With the geometry described heretofore, Reynoldsnumbers as great as 7500 and Dean numbers as great as 1000 are expectedwith ratios of ZR Ir of about 1:14. in summary, optimum flow withoutturbulence is a function of (R,, L/W, D, VXR).

Thus, the design sequence is to select a magnet core mean radius andcross section. The radius of the duct r will have to correspond with theradius of the core and the radial length of the core will have to be thesame as L of the duct. Since the ratio of L:W is preferably about 5:1the width W of the duct can be established. Now the Dean number has aratio of 2R :r in which case the above design sequence dictates a ratioof about 1:14. This ratio would remain the same regardless of thedimensions and capacity. The critical Reynolds number above whichturbulence might occur depends on 2R zr.

At 1:14 the critical Reynolds number is about 7500.

Since laminar operation is required, a maximum Dean number of about 1000is expected. Models tested have had best separation of particles atlower Dean numbers, as low as 80, but tests show that if the product offluid velocity V and flux B are made larger, best separation will occurat Dean numbers much greater than up to about 1000.

The embodiment of the invention shown in FIG. 1 has the faces 19 and 20of the cup-shaped magnetic pole pieces 17 and 18 on opposite axiallyseparated sides 43 and 44 of the main duct 40. The magnetic lines offorce thus extend across'the air gap 21 and through duct 40 in an axialdirection. This results from the diameters of the pole pieces 17 and 18being equal in which case it is most convenient to interpose the ductbetween the pole faces. it should be understood, however, that otherarrangements of thepolepieces may be used to create an air gap acrosswhich the magnetic flux is projected and in which a non-magnetic ductmay be located. For instance, the diameter of one pole piece such as 17may bemade considerably smaller than the internal diameter of the other18 in which case the former may be fit axially within the other and theannular air gap so created may be occupied by a circular duct as in thepresent case. The different direction of magnetic flux with respect tothe direction of magnet rotation would, of course, result in the chargedparticles being deflected primarily in opposite axial directions ratherthan radially as in the abovedescribed embodiment.

Permanent magnets can also be used for generating a rotating magneticfield in which case one may take the form of a shaft mounted disk thatis inside of the circular duct opening and the other may be essentiallya ring which is also on the shaft but outside of the circular duct. Thepole pieces may also be fabricated from individual magnet segments withnon-magnetic circumferentially spaced gaps between them if desired. Theelectromagnetic poles may also be made as spoked wheels with a segmentedrim. The magnet coils may be wound on the spokes of magneticallypermeable material. The magnetic field may, in any case, be caused torotate in a horizontal plane about a vertical axis and the duct may behorizontally oriented instead of vertically as shown herein.

possible to split the duct into two substantiallysemi-circularadjacentduct sections which each have an inlet at one end and an exit analyzerat the opposite end, the V inlet of one duct section being diametricallyopposite from the inlet of theother section and theme being true of theexit ports. The ducts may also be nearly full 1 circles and arrangedadjacent each other or concentrically, the object being of course, toreduce the critical Reynolds number R by reducing the hydraulic radius Rv In large capacity particle separators a greater total volume of fluidis passed through the duct but it is still desirable to maintain the lowReynolds numbers of smaller machines in order to assure laminar ratherthan turbulent flow. Thus, in large separators the duct can besubdivided cross sectionally to create two or more parallel paths whichare coextensive in length and really constitute individual curvedadjacent ducts ina common magnetic field. Each of thedUCtSllbdiViSiOl'lS will have its own multiple port means as, in thecases described above where only one duct was employed,

FIG. 6 shows a fragment of a curved alternative form of duct which issubdivided or partitioned longitudinally and FIG. 7 shows a crosssection of it. Thus, there are radial and transverse partition walls 101and 102 respectively, defining in this case four parallel curved ducts103-106. It will be understood that each duct will have its own inlet,analogous to' 56 in FIG. 1, and its own multiport means analogous tothose shown in FIGS. 3-5 or they may have other forms. This multichannelduct will be interposed between rotating magnets as is the case with thesingle duct in FIG. 1.

As mentioned heretofore, some suspended fine particles are notinherentlycharged andrnust have a charge induced. This is accomplishedeasily by running the fluid suspension through a pipe made of insulatingmaterial in which there are at least a pair of transverse metal screensspaced from each other by about an inch. Each screen is connected to anopposite polarity terminal of a d-c source which will have low voltagein any case and should be about 1.5 volts forwatersuspensions. As thefluid suspension flows through the screens its particles adopt achargeafterwhich the suspension is fed to the particleseparator ductinlet.

In summary, the new electrodynamic particle separator is characterizedby having a rotating magnet'act on a rotating stream of charged fluidentrained particles at optimum relative rotational speeds. The particlesare conducted through a duct which terminates in a transversemultiported means that separates the concentrates and dilute streams inconformity with the manner in which these streams are generated in theduct.

Although an embodiment of the invention has been described inconsiderable detail, such description is to be variously embodied and isto be limited only by interpretation of the claims which follow.

l. A Lorentz-force method of concentrating fluid suspendedchargedparticles in a stream that is separable from the more dilute fluidstream, said method comprising:

a. admitting said charged particle containing fluid into a curvedsubstantially nonconducting and nonmagnetic duct so that the, fluidflows-around the interior of the duct in a direction that issubstantially normal to a cross sectional plane of the duct,

b. disposing magnetic pole pieces having opposite polarity on oppositesides of the duct to produce a magnetic flux which is substantiallyuniform about.

the fluid flow path during rotation and has a vector substantiallynormal in direction to the flow direction of the fluid, 1 c.rotatingsaid magnetic pole pieces along a curved path defined by theduct at a velocity which is high compared to the fluid velocity andwhich has a velocity vector substantially normal to said flux vector tothereby produce an intense Lorentz force to cause the charged particlesto migrate substantially normal to the'plane defined by the velocityvector ofthe flux and flux vector thereby causing the fluid stream toseparate into concentrate and dilute portions, and

- I d. passing said portions through ported separating means interposedtransverse to the fluid flow direction in a curved part of the duct.whereby to 3 permit exiting the dilute and concentrate portions from theduct insubstantially separate paths.

2. The method set forth in claim 1 wherein:

a. said magnetic flux is rotated at a rate in the range of about 1000 toabout 100,000 revolutions per minute. 3; The method set forth in claim 1wherein: a. the magnetic field is moved at a linearvelocity in V therange of to 1000 feet per second.

4. The method set forth in claim 1 wherein:

a. the flux density of the magnetic field isin the range of 1000 to25,000 gausses.

SPApparatus for concentrating charged particles ina fluid suspensionwith Lorentz forces and for separating the concentrates from the moredilute part of the suspension comprising:

a.. a curved duct means of nonconducting and nonmagnetic material, saidduct means having a fluid inlet and an exit region angularly displacedwithin the ductmeans from said inlet,

b. magnetic .polemeans of opposite polarity on opposed sides of the ductmeans for producing a substantially uniform magnetic flux along thefluid flow path during rotation which has a vector that is directedsubstantially normal to the fluid flow direction within the duct means,

c. means for rotating said pole means jointly about the duct at highangular velocity whereby the flux has a velocity vector substantiallynormal to said vector to produce an intense Lorentz force on the chargedparticles causing them to migrate substan-,

tially normal to the plane of the flux vector and the velocity vector ofthe flux in the duct means to form concentrate and dilute streams,

d. multiport means disposed transversely to the fluid flow path in acurved part of the duct means and near the exit region thereof, at leastone of the ports being positioned to pass a concentrate stream and atleast anotherof said ports being positioned to pass a more dilutestream.

6. The invention set forth in claim wherein:

a. said duct means has a radially extending fluid outlet means locatedbeyond said port means in a direction of fluid flow, said outlet meanshaving isolating channel means for directing the concentrate and dilutestreams out of the duct means.

7. The invention set forth in claim 6 including:

a. valve means communicating with said channel means for regulating theflow volume of the concentrate and dilute streams.

8. The invention set forth in claim 5 wherein said port means ischaracterized by it having:

a. a substantially central dilute stream port, and

b. concentrate stream ports which have dimensions radially of said ductmeansthat are less than the radial dimension of said dilute stream port,said concentrate stream ports being located radially inwardly andoutwardly, respectively, from said dilute stream port.

9. The invention set forth in claim 5 wherein said port means ischaracterized by it having:

a. a radially and axially bounded substantially central dilute streamport, and

b. an annular concentrate stream port surrounding said dilute streamport.

10. The invention set forth in claim 5 wherein said port means ischaracterized by it having:

a. at least two central dilute stream ports being elongated radially andbeing axially spaced from each other to define a central radiallyextending concentrate stream port therebetween, and

.b. a continuous narrow concentrate stream port surrounding said dilutestream ports and said radially extending concentrate stream port.

11. The invention set forth in claim 5 including:

a. a shaft on which said pole pieces are positioned in spacedrelationship to create a flux gap in which '14. The invention set forthin claim 5 wherein:

a. the internal dimension of the duct means in the direction betweensaid pole pieces is defined as L and the dimension of the duct meansperpendicu lar to L is defined as W and the range of ratios between LandWis 1.5:1 to 5:1.

15. The invention set forth in claim 5 wherein:

a. the range of area ratios for said dilute stream port to saidconcentrate stream port is 1.5:] to 5:1.

16. The invention set forth in claim 5 wherein:

a. the range of ratios between 2R,,/r is between I and 14 where R is theh drau ic r dius of said duct means and r'is the meai n radius ofcurvature of said duct means.

17. The invention set forth in claim 5 wherein:

a. said pole piece rotating means rotates the same at a rate in therange of 1000 to 100,000 revolutions per minute.

18. The invention set forth in claim 5 wherein:

a. the linear velocity vector of said flux is in the range of to 1000feet per second.

19. The invention set forth in claim 5 wherein:

a. said flux is in the range of 1000 to 25,000 gausses.

20. The invention set forth in claim 5 wherein:

a. the said pole means on opposed sides of the duct means each havemagnetic material faces adjacent the duct means which faces aresubstantially continuous in a direction about their rotational axis tothereby produce a magnetic flux which is substantially uniform aroundthe duct means when the pole means are rotated.

UNITED STATES PATENT OFFICE cERTiFIcATE OF coRREc'iioN Patent No. 3,693,792 Dated SEPTEMBER 26, 1972 Inventofls) JAMES I. LANG 7 It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In claim 12 add the following: ---b) a shaft on which said pole piecesare mounted,

c) electromagnet coil means in the concave space of the pole pieces, andd) slip rings mounted to rotate with said shaft and connected toopposite ends respectively of said coil means.

Assignment should indicate: --Undivided 1/2 interest to John F.Sylvester.

Signed and sealed this 3rd day of April 1973.

{SEAL} Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. A Lorentz-force method of concentrating fluid suspended chargedparticles in a stream that is separable from the more dilute fluidstream, said method comprising: a. admitting said charged particlecontaining fluid into a curved substantially nonconducting andnonmagnetic duct so that the fluid flows around the interior of the ductin a direction that is substantially normal to a cross sectional planeof the duct, b. disposing magnetic polE pieces having opposite polarityon opposite sides of the duct to produce a magnetic flux which issubstantially uniform about the fluid flow path during rotation and hasa vector substantially normal in direction to the flow direction of thefluid, c. rotating said magnetic pole pieces along a curved path definedby the duct at a velocity which is high compared to the fluid velocityand which has a velocity vector substantially normal to said flux vectorto thereby produce an intense Lorentz force to cause the chargedparticles to migrate substantially normal to the plane defined by thevelocity vector of the flux and flux vector thereby causing the fluidstream to separate into concentrate and dilute portions, and d. passingsaid portions through ported separating means interposed transverse tothe fluid flow direction in a curved part of the duct whereby to permitexiting the dilute and concentrate portions from the duct insubstantially separate paths.
 2. The method set forth in claim 1wherein: a. said magnetic flux is rotated at a rate in the range ofabout 1000 to about 100,000 revolutions per minute.
 3. The method setforth in claim 1 wherein: a. the magnetic field is moved at a linearvelocity in the range of 100 to 1000 feet per second.
 4. The method setforth in claim 1 wherein: a. the flux density of the magnetic field isin the range of 1000 to 25,000 gausses.
 5. Apparatus for concentratingcharged particles in a fluid suspension with Lorentz forces and forseparating the concentrates from the more dilute part of the suspensioncomprising: a. a curved duct means of nonconducting and nonmagneticmaterial, said duct means having a fluid inlet and an exit regionangularly displaced within the duct means from said inlet, b. magneticpole means of opposite polarity on opposed sides of the duct means forproducing a substantially uniform magnetic flux along the fluid flowpath during rotation which has a vector that is directed substantiallynormal to the fluid flow direction within the duct means, c. means forrotating said pole means jointly about the duct at high angular velocitywhereby the flux has a velocity vector substantially normal to saidvector to produce an intense Lorentz force on the charged particlescausing them to migrate substantially normal to the plane of the fluxvector and the velocity vector of the flux in the duct means to formconcentrate and dilute streams, d. multiport means disposed transverselyto the fluid flow path in a curved part of the duct means and near theexit region thereof, at least one of the ports being positioned to passa concentrate stream and at least another of said ports being positionedto pass a more dilute stream.
 6. The invention set forth in claim 5wherein: a. said duct means has a radially extending fluid outlet meanslocated beyond said port means in a direction of fluid flow, said outletmeans having isolating channel means for directing the concentrate anddilute streams out of the duct means.
 7. The invention set forth inclaim 6 including: a. valve means communicating with said channel meansfor regulating the flow volume of the concentrate and dilute streams. 8.The invention set forth in claim 5 wherein said port means ischaracterized by it having: a. a substantially central dilute streamport, and b. concentrate stream ports which have dimensions radially ofsaid duct means that are less than the radial dimension of said dilutestream port, said concentrate stream ports being located radiallyinwardly and outwardly, respectively, from said dilute stream port. 9.The invention set forth in claim 5 wherein said port means ischaracterized by it having: a. a radially and axially boundedsubstantially central dilute stream port, and b. an annular concentratestream port surrounding said dilute stream port.
 10. The invention setforth in claim 5 wherein said port meaNs is characterized by it having:a. at least two central dilute stream ports being elongated radially andbeing axially spaced from each other to define a central radiallyextending concentrate stream port therebetween, and b. a continuousnarrow concentrate stream port surrounding said dilute stream ports andsaid radially extending concentrate stream port.
 11. The invention setforth in claim 5 including: a. a shaft on which said pole pieces arepositioned in spaced relationship to create a flux gap in which saidduct means is positioned.
 12. The invention set forth in claim 5wherein: a. said pole pieces are concave and are in opposedrelationship, the ends of said pole pieces constituting annular polefaces which are axially spaced from each other to define a magnetic fluxgap in which said duct means is disposed,
 13. The invention set forth inclaim 5 including: a. means subdividing the aforesaid duct means intoindividual duct means which are substantially coextensive with theaforesaid duct means.
 14. The invention set forth in claim 5 wherein: a.the internal dimension of the duct means in the direction between saidpole pieces is defined as L and the dimension of the duct meansperpendicular to L is defined as W and the range of ratios between L andW is 1.5:1 to 5:1.
 15. The invention set forth in claim 5 wherein: a.the range of area ratios for said dilute stream port to said concentratestream port is 1.5:1 to 5:1.
 16. The invention set forth in claim 5wherein: a. the range of ratios between 2RH/r is between 1 and 14 whereRH is the hydraulic radius of said duct means and r is the mean radiusof curvature of said duct means.
 17. The invention set forth in claim 5wherein: a. said pole piece rotating means rotates the same at a rate inthe range of 1000 to 100,000 revolutions per minute.
 18. The inventionset forth in claim 5 wherein: a. the linear velocity vector of said fluxis in the range of 100 to 1000 feet per second.
 19. The invention setforth in claim 5 wherein: a. said flux is in the range of 1000 to 25,000gausses.
 20. The invention set forth in claim 5 wherein: a. the saidpole means on opposed sides of the duct means each have magneticmaterial faces adjacent the duct means which faces are substantiallycontinuous in a direction about their rotational axis to thereby producea magnetic flux which is substantially uniform around the duct meanswhen the pole means are rotated.